1. Field of the Invention
The present invention relates to an ink-jet printing method, comprising the steps of printing an image with at least one ink on a recording medium; and applying a cover liquid on the image formed with the at least one ink within 1 s after printing the image with the at least one ink. The present invention also relates to an ink-jet printing apparatus, comprising at least one printing unit configured to print an image with at least one ink on a recording medium; and an application unit configured to apply a cover liquid on the image formed with the at least one ink.
2. Description of Background Art
During printing of inks, e.g. latex inks, two colors touch each other, bleeding can occur, i.e. a macroscopic flow of ink from one “color” into another. This effect creates unsharp boundaries between different colors on a print, which is unwanted.
Possibilities to overcome the bleeding problem have been analyzed from different points of view of the printing process.
In this regard, U.S. Pat. No. 8,083,339 discloses a treating liquid that is to be applied before printing of a recording liquid. However, the treatment liquids disclosed contain crashing agents (coagulation agents; destabilization agents; which are compounds reactive with an ink component) for pinning purposes.
U.S. Pat. No. 7,645,036 discloses a treatment liquid and ink combination, wherein the reaction liquid is applied prior to the ink compositions. However, the disclosed inks are curable ink compositions. Furthermore, the reaction liquids also contain curable compounds.
Taken together, U.S. Pat. No. 7,645,036 describes an ink spread suppressing liquid, and U.S. Pat. No. 8,083,339 describes a treating liquid, both liquids being printed before printing of the recording liquid and having both a lower surface tension than the recording liquid in order to reduce image bleeding. However, both methods have the disadvantage that the treating liquid interacts with the recording medium and that the treating liquids contain further substances that are undesirable in the printing process. In addition, the treating liquids disclosed in these two documents spread more than the recording liquids applied on top of the treating liquid.
In addition, U.S. Patent Application Publication No. 2014-171558 A1 describes a method for printing wherein bleeding is resolved by variations on the same two principles: either it is prevented by some mechanism involving increased penetration of the ink into the medium, and thus preventing inter-color bleed, or it is prevented by a destabilization mechanism—i.e. precipitation on the surface with a primer—of a pigment or a polymer in an ink which “locks” the color into place on the medium, thus preventing bleeding. This comes at a cost, though, as increasing the penetration of inks can lead to low optical density or strike-through of the print. Further, the destabilization mechanism precludes the use of stable pigments or the use of dye inks. It demands a reaction liquid and an ink which have been specifically tuned to each other. Often, these systems use salts or other ionic moieties which can be destructive for the printhead, e.g. due to corrosivity.
Therefore there is a need for a simple ink-jet printing method that can efficiently prevent bleeding without requiring a special pre-treatment of the recording medium and special agents used therefore, which can be detrimental to the printing method and/or the printing apparatus.